A French naval vessel is joining the hunt for "black boxes" from the EgyptAir passenger jet which crashed in the eastern Mediterranean Sea on May 19, according to France's BEA air-crash-investigation agency.

The BEA said the La Place left Corsica on Thursday and was heading towards the search zone north of the Egyptian port of Alexandria, where it would begin operations within days.

"A deep-water search campaign will begin in the coming days with the arrival in the accident area of the French navy surveillance vessel La Place," said the BEA.

Meanwhile, hundreds of people gathered in Cairo for a candlelit vigil for the victims of the air crash.

Sherif Fathy, Egypt's civil aviation minister, said it was a mark of respect to the victims and their families.

Mix of nationalities

Among those on board flight MS804 were 30 Egyptians, 15 French citizens, two Iraqis, two Canadians and citizens from Algeria, Belgium, Britain, Chad, Portugal, Saudi Arabia and Sudan.

They included a boy and two babies as well as seven crew and three security staff.

Two BEA investigators were on board the La Place as it set sail from Corsica on Thursday.

The vessel is equipped with three deep-water devices known as Detector 6000s that can detect the black boxes' signals, the French agency said.

It said the Egyptian authorities "will be piloting these underwater searches" with the BEA's help.

Talks are still under way to add to the mission a second vessel equipped with a deep-sea exploration robot and the recovery capabilities required to work at an estimated depth of 3,000 metres.

On Wednesday, the French foreign ministry said France and Egypt would hire two private firms to help in the hunt for the flight recorders.

Race against time

France and Egypt will share the costs for the search, which faces a race against the clock, as the flight data and voice recorders emit locator "pings" for no more than about a month.

DOS says it can operate in depths of up to 6,000 metres and has a robot that is capable of mapping the seabed.

Egypt has deployed a submersible that can operate at a depth of 3,000 metres in the hunt for the black boxes, while a French patrol boat is also in the search area, concentrating mainly on the surface.

France's aviation safety agency has said the aircraft transmitted automated messages indicating smoke in the cabin and a fault in the flight control unit before contact was lost.